1. Field of the Invention
The present invention relates to an invisible information recorded medium on which invisible information has been recorded, a detecting apparatus for detecting the invisible information and a recording agent for recording the invisible information.
2. Related Background Art
(1) Hitherto, the trend of improving the performance of copying machines arises a risk of forgery of bills, securities and notes and the like. Therefore, there arises a necessity of judging whether or not forgery of the bill or the like has been performed. Further, the forgery of the bills must be previously detected and prevented. In order to prevent the forgery, there have suggested a marking method using a ultraviolet ray exciting fluorescent pigment, a method using a diffraction phenomenon such as hologram, a method of applying a magnetic substance to be detected by a magnetic head, a method using color change occurring due to photochromism and a method of discriminating a specific image, such as a bill, by image recognition.
(2) With the improvement in the performance of the copying machine and so forth, copying of various information items can easily be performed.
On the other hand, privacy guarding and trade secret confidence have been considered important, causing a problem to arise in that copying can easily be performed.
Hitherto, the foregoing copying has been prevented by bonding a special film to the document or the like to cause the copied image to be deteriorated or to cause the forgery to be informed.
(3) A method has been known which is arranged in such a manner that an image is formed on the surface of a photoconductive material by an electrostatic method and then the image is developed. As disclosed in U.S. Pat. No. 2,297,691 filed by C. F. Carlson, the basic electrophotographic method comprises the steps of uniformly loading static electricity onto a photoconductive insulating layer, exposing the layer to a light and dark image to delete the electric charge of the region exposed to light, and allowing fine substance called a toner to adhere to an electrostatic latent image thus-obtained so that the foregoing electrostatic latent image is developed.
The toner is usually attracted to a region of a layer in which the charge is left, causing a toner image corresponding to the electrostatic latent image to be formed.
Then, the thus-formed powder image can be transferred onto the surface of a supporting member, such as paper. The transferred image can permanently be secured onto the surface of the supporting member with, for example, heat.
In place of forming the latent image by uniformly charging the layer of the photoconductive layer and by exposing the layer to the light and dark image, the latent image may be formed by directly charging the layer in the form of the image.
If the process of transferring the powder image is intended to be omitted, the powder image may be secured to the photoconductive layer. Another method may be employed in which an adequate fixing means, such as solvent treatment or outer layer coating process, is employed in place of the heat fixing process.
There have been some known methods of using toner particles as the electrostatic latent image to be developed. One of the developing methods has been disclosed in U.S. Pat. No. 2,618,552 filed by E. N. Wise which is a cascade development method.
The cascade development method comprises the steps of carrying a developer composed of relatively large carrier particles having fine tone particles electrostatically coated on the carrier to the surface of electrostatic latent image carrying surface as to be rolled or cascaded.
The composition of the carrier particles is so selected that the toner particles are charged in a frictional charge manner to a desired polarity.
When the mixture is cascaded or rolled while exceeding the development carrying surface, the toner particles are allowed to electrostatically adhere and secure to the charged portion of the dissolved image but the same does not adhere to the portion, in which the image is not charged, that is, the base portion.
The toner particles accidentally allowed to adhere to the base portion are substantially removed with the rolling carrier due to a fact that the electrostatic attractive force between the toner and the carrier is larger than that between the toner and the non-charged base portion.
The carrier and the excess toner are then recirculated. The foregoing method is significantly effective to develop a linear copied image.
Another method for developing the electrostatic image is a magnetic brush method as disclosed in, for example, U.S. Pat. No. 2,874,063. The foregoing method comprises the step of carrying a developing substance containing a toner and magnetic carrier particles with a magnet. The magnetic field of the magnet arranges the magnetic carrier to be formed into a brush-like shape. The magnetic brush comes in contact with the surface of the electrostatic image carrying surface, causing the toner particles to be attracted from the brush to the latent image with the electrostatic attractive force.
Another method capable of developing the electrostatic latent image is a powder cloud method as disclosed in, for example, U.S. Pat. No. 2,221,776 filed by C. F. Carlson. The foregoing method comprises the step of allowing to pass a developing substance containing electrically charged toner particles in a gaseous fluid through a position adjacent to the surface carrying the electrostatic latent image. The toner particles are attracted from the gas to the latent image by the electrostatic attractive force. The foregoing method is significantly effective to develop an image in which light portions and dark portions are distributed continuously.
A touch-down method disclosed in U.S. Pat. No. 3,166,432 filed by R. W. Gundlach may be employed if necessary.
Among the foregoing available methods, the magnetic brush method has been widely used.
Although the foregoing methods are used to make a black and white copied product, they are able to form an image in another color or an image formed by combining colors.
Similarly to another coloring method, an electrophotographic coloring method is usually based on a color-additive or subtractive color formation type synthesis of three colors. That is, if the electrophotographic method is performed in a full color manner, three or more color toners, that is, developing particles must be used to synthesize any desired color.
In order to color-copy a full-color original, three or more color decomposed images are mutually matched and combined with one another. In the color electrophotography, three or more electrostatic images are, as described above, generated by exposing a photosensitive member to an optical color decomposed image as disclosed in, for example, U.S. Pat. No. 2,962,374.
The electrostatic latent images respectively are developed by different color toners, and then the three-type toner images are combined with each other so that a final image is formed. The combination of the three color toner images are usually formed on a copying sheet, such as paper, and the toner image is permanently fixed on the sheet.
The most ordinary method for fixing the toner images on a paper copying sheet is a method comprising the steps of using a resin toner containing a coloring agent and fusing the toner image onto the copying sheet with heat.
The image may be fixed by another method, for example, it is exposed to molten vapor. With the progress of the copying method, information confidence becomes an important fact.
Forgery copying has been prevented by a method comprising the step of bonding a special film to the document or the like to deteriorate the quality of the copied image or a method of clearing the forgery copying.
(1) However, the method using the ultraviolet rays exciting fluorescent pigment encounters a problem in that a countermeasure can be taken because the fluorescent pigment can easily be detected by an ultraviolet irradiation means, such as a black lamp. Further, the necessity of using a ultraviolet ray source in the apparatus makes the optical system to be complicated. The method using the diffraction phenomenon, such as hologram, encounters a problem in that the formation of the mark on the bill or the like raises the cost. The method of applying the magnetic substance arises a necessity of bringing the bill or the like into contact with the magnetic head in a hermetical manner, causing a problem to arise in that the structure to be complicated. The method using photochromism suffers from instability of the photochromism compound. The method based on the image recognition requires a large quantity of data to recognize all bills and securities and so forth, causing a heavy load to be burden by the apparatus and the cost to be enlarged.
Another method using near infrared fluorescent has been disclosed to overcome the foregoing problems, so that a long life light emitting diode is enabled to be used, and therefore an influence of contamination can be prevented satisfactorily.
If the near infrared ray absorbing film or the like is used between the detecting apparatus and the original document, there arises a problem in that the detection cannot easily be performed. The necessity of individually using a light emitting diode and a photodiode sensitive to long wavelength causes the structure of the apparatus to be complicated.
(2) However, each of the foregoing conventional methods has been structured to correspond to analog copying machines. Therefore, it has been difficult to prevent the forgery copying and reading in a copying machine or a printer comprising a reading unit using a CCD or the like.
Therefore, it is preferable that the detection apparatus identifies that the recorded medium is the copy and read inhibited medium to stop the operation.
Each of the foregoing identifying marks has a problem.
(3) However, each of the foregoing conventional methods has been structured to correspond to analog copying machines. Therefore, it is unsatisfactory to realize secret confidence with a copying machine or a printer comprising a reading unit using a CCD or the like. The fact that the easy recognition arises a problem in that an effective secret confidence method has not been realized against reproduction writing and photography.